A British piano tuner is about to share a six-figure reward for discovering a stash of 913 gold coins hidden beneath the keyboard of an upright that had been donated to a community college. The gold sovereigns, which date from 1847 to 1915, have a face value of £773, which is equivalent to £500,000 ($640,000) today.

Martin Backhouse, 61, had been hired by Bishop’s Castle Community College in Shropshire, England, to work on a Broadwood & Sons piano that had been donated to the school by the Hemmings family. The piano was made in 1906 and the Hemmings family had owned the instrument for 33 years.

"I had only taken out the first octave when I realized something was going on," Backhouse told the Daily Mail.

The piano tuner discovered seven cloth-bound packets and a leather drawstring purse under the keyboard. He was shocked to learn that each was filled with gold sovereigns and half sovereigns, the majority dating to the reign of Queen Victoria. Experts at The British Museum believe the coins — now called the Piano Hoard — were tucked away in the late 1920s, perhaps in reaction to the Great Depression or the events leading up to World War II. Cardboard lining from one of the packages suggests the hoard was hidden between 1926 and 1946. The identity of the original owner is still a mystery.

As is required by the British Treasure Act of 1996, Backhouse and college officials reported their find to the local coroner. The sovereigns were declared to be treasure at an inquest at Shrewsbury Coroner's Court, and this meant that Backhouse and the college could be compensated for the value of the coins as determined by the Treasure Valuation Committee. The Treasure Act allows for a reward to be shared among the finder and the owner of the land on which the treasure was found. The Treasure Act is administered by staff at The British Museum.

Normally, treasure is considered to be more than 300 years old and made of gold or silver. Although the Piano Hoard was not nearly that old, the Treasure Act also states that items of any age made substantially of gold or silver, whose original owners or heirs are unknown, and which are deemed to have been deliberately hidden with the intention of recovery, are also "treasure."

"The individual coins are not particularly rare being the button coinage of the British Empire," noted a spokesperson for The British Museum. "However, it is the largest hoard of its type known and the find is of significant importance from a historical perspective. It is a fascinating story. We are not aware of any other coin hoards being secreted in pianos."

While Backhouse and the college are likely to share hundreds of thousands of dollars, the piano's most recent owners — the Hemmings family — are entitled to nothing under British law.